1. Field of the Invention
The present invention relates to a determination method and apparatus for permitting deceleration regeneration or charge of a hybrid vehicle which has an electric motor as a power generating mechanism, in addition to the engine.
2. Description of the Related Art
From recent viewpoints relating to the protection of environment or the saving of energy, the so-called cylinder direct-injection engine for directly jetting fuel into the cylinder of the engine has been put to practical use as a power generator for vehicles such as cars. Currently, hybrid vehicles having a combined power system consisting of such an engine and an electric motor for driving are being developed.
As a hybrid vehicle, a parallel hybrid vehicle is known, which uses an electric motor as an auxiliary drive source for assisting the engine output. An example thereof is disclosed in Japanese Unexamined Patent Application, First Publication, No. Hei 7-123509. In the disclosed system, the engine output is assisted using the electric motor in the accelerating operation (i.e., acceleration mode), while in the decelerating operation (i.e., deceleration mode), the battery and the like are charged via a regenerating operation, that is, "deceleration regeneration" is performed. According to various control operations including the above, the remaining capacity of the battery is maintained while the driver's demands can also be satisfied.
In the deceleration regeneration, the electric motor is driven in reverse by the rotational force of the driving wheels so that the motor functions as a generator. In a parallel hybrid vehicle employing a manual transmission in which the output shaft of the engine and the output shaft of the electric motor are directly coupled, if the clutch is disconnected (or disengaged) during the deceleration-regenerating operation, the driving wheels do not drive the electric motor, so that all the torque generated by the electric motor functions as a load imposed on the engine. Generally, in the deceleration mode, the degree of opening of the throttle valve is small and the engine output is low. Therefore, if the deceleration regeneration is performed under such conditions, the torque generated by the electric motor is transmitted to the engine side as an excessive load. As a result, the engine (rotational) speed may decrease remarkably, or the engine may stall.
On the other hand, when the clutch is connected (or engaged) during the deceleration-regenerating operation, almost all of the torque generated by the electric motor is obtained by the rotational torque of the driving wheels; therefore, the torque generated by the electric motor is not applied to the engine side as a load in practice. Therefore, in the deceleration regeneration, the engine speed does not decrease remarkably and the engine does not stall.
Accordingly, when a conventional hybrid vehicle employing a manual transmission executes deceleration regeneration, the respective states of the gear and clutch are detected and it is determined whether the output shaft of the engine and the driving wheels are coupled with each other. When the clutch is connected and the vehicle is in gear, that is, when the electric motor is coupled with the driving wheel side, deceleration regeneration is permitted.
In such a hybrid vehicle employing a manual transmission, if the clutch is half connected (i.e., the clutch is halfway in) by the driver's operation in the deceleration mode, an erroneous determination that the clutch is connected may occur though the clutch is actually disconnected. As a result, deceleration regeneration is permitted and executed, so that the engine speed may decrease remarkably, or the engine may stall.
The relevant mechanism will be explained with reference to FIGS. 5 and 6.
Generally, in a vehicle employing a manual transmission, if the clutch is connected, for example, when the cranking of the engine is performed so as to start the engine, the vehicle may erroneously start due to the cranking. In order to prevent such an unexpected phenomenon, clutch switch S.sub.5, set to on when clutch pedal 9 is depressed, is attached to a supporting member of the clutch pedal 9 (refer to FIG. 5), and cranking is permitted if the clutch switch S.sub.5 is on.
In FIG. 5, line A indicates the depressed position (or degree) of clutch pedal 9 when the clutch is actually disconnected, while line B indicates the depressed position (or degree) of clutch pedal 9 when the clutch switch S.sub.5 is set to on. As shown in the figure, the degree of depression of line B is larger than the degree of depression of line A. Therefore, even if the clutch becomes worn down and the clutch contact is shifted, it is possible to reliably detect the state that the clutch is completely disconnected, and to reliably prevent an unexpected phenomenon such as the erroneous start caused by the cranking.
On the other hand, in order to execute the above-explained deceleration regeneration, the clutch must be connected so as to transmit the rotational torque of the driving wheel side to the output shaft of the electric motor (used for driving). Therefore, the connection state of the clutch must be detected. Accordingly, when determining whether the deceleration regeneration should be permitted in a hybrid vehicle, the connection state of the clutch is detected using the above-described clutch switch S.sub.5. In the determination, deceleration regeneration is permitted when the clutch switch S.sub.5 is off.
However, in the deceleration mode, if the depressed clutch pedal 9 is positioned between line A and line B of FIG. 5 (for example, when the clutch is half connected), it is determined that the clutch is connected though the clutch is actually disconnected, as described above. Therefore, a result of an erroneous determination to permit the deceleration regeneration is output. Accordingly, an excessive regeneration load is applied to the engine in the deceleration driving state (or the idling state), which may cause a remarkable decrease in the engine speed, engine stall, or the like.
Similar problems may occur in the cruising operation.
That is, if the clutch pedal 9 is depressed and is positioned between the above lines A and B while the engine is driven at low engine speed, it is determined that the clutch is connected though the clutch is actually disconnected, so that an erroneous determination to permit the charging operation is made. As a result, an excessive charge load is applied to the engine in the cruise driving state (i.e., low output state), which may also cause a remarkable decrease in the engine speed, engine stall, or the like.